The major function of an ordinary hydraulic actuator is to use hydraulic energy (produced by hydraulic source, i.e. pumps) to carry loading into linear, reciprocating or other types of mechanical operations. For example, hydraulic jacks are used to lift a load to a required height, however the lifting speed of actuator is constant in heavy loading, light loading or without loading conditions.
An ordinary jack wastes time and effort while the actuator is under light loading or no loading condition because the lifting speed is limited by the hydraulic pressure which is rated for heavy loading condition. The lifting speed should be faster while in no loading or light loading to minimize the time required for lifting its load. Therefore the ordinary actuator design cannot utilize to full advantage the hydraulic energy to speed up the lifting operation to save time and effort.